Solar cells with compounded semiconductor films are one of the most efficient and potential thin-film solar cells. Compound semiconductor material has the highest light absorption coefficient in known semiconductor materials, which may reach up to 105/cm, without semiconductors having S-W effect (Staebler-Wronski Effect). Moreover, converting efficiency thereof may be enhanced by light irradiation. Therefore, this kind of solar batteries may have a long lifespan. It is shown by experiments that compound semiconductor film solar batteries have even longer life span than monocrystalline silicon batteries which may last for normally 40 years. The compound semiconductor is a direct band gap semiconductor material, which is most suitable for film.
Currently, there are many methods for preparing a compound semiconductor film. To overcome disadvantages of the method in the prior art, a vacuum evaporating method was brought forward.
The vacuum evaporating method means that the source material is heated in a container in the vacuum conditions so that atoms or molecules are evaporated or escaped from the surface and form a steam flow onto the surface of the substrate and then condense into a solid thin film. The compound semiconductor thin film solar cell prepared thereof may have high converting efficiency. However, the cell area prepared is far less than 1 cm2, which is mainly limited by emitting characteristics of the evaporation source. While preparing thin film with a large area, the coating material distribution is severely uneven. The larger the scale is, the more uneven the material distribution is. Due to the large area requirement to for the solar cell, this method does not have industrial commerciality.
To improve the method, line movement of the substrate is suggested, with rod-shaped evaporation source for vapor-depositing to form the coating film. Although semiconductor film with a relatively large area may be achieved in this case, the uniformity thereof is still low, normally around ±10%. However, the rod-shaped evaporation source is hard to prepare, because the rod-shaped source shall have the same temperature in each part thereof for uniform evaporation, and shall have no slower or faster evaporation parts existing herein. However, the internal defect distribution inside the evaporation source may affect the evaporating speed or cause slower or faster evaporation at certain parts. Therefore, it is very complex for theoretical calculation to the rod-shaped evaporation source which is hard for processing. Further, the whole apparatus is expensive and needs precise control.